Curtain walls (or cut-off walls as they are sometimes called) are extensively used as a means of separating or confining sources or potential sources of liquids or gases to prevent migration or mixing with the remainder of the environment. In their simplest form, curtain walls consist of a generally vertical barrier or restriction to lateral fluid flow. The barrier may be placed in a trench or otherwise installed across the potential route of fluid migration. The trench is most desirably of sufficient depth to reach and be sealed to a relatively impermeable strata at the lower extremity, thus providing a seal against egress of the media to be confined. This confinement is carried out so as to prevent or significantly reduce the spread of contaminants that might pollute the adjoining environment.
Various media have been used to form this barrier. This media includes materials such as clay and bentonite. More recently, synthetic membranes, such as high density polyethylene, have been used for this purpose. The membrane may be used independently or in conjunction with other barrier materials. The choice of high density polyethylene is based on its unique composition of properties of high mechanical strength, deformability, corrosion resistance, resistance to biological attack, impermeability to leachate and landfill gas, and extended service life. Other flexible membranes may also be used, if they are suitably resistant to degradation and/or permeation by the fluid t o be confined.
The high density polyethylene membranes, which are used in cut-off wall applications, are usually of a thickness of approximately 1.0 to 2.0 mm to provide sufficient mechanical strength to absorb forces encountered both in installation and in operation, to contain resulting strains within acceptable limits. Membranes of other thicknesses may be used to provide a service life consistent with the specific design purpose. Protection for the membrane such as a geotextile or selected backfill material may also be utilized in conjunction with the membrane. Where bentonite is used in the exacavation of the trench, this material also provides protection for the membrane as well as an additional sealant against fluid flow.
In certain circumstances, such as short, straight, and shallow cut-off trenches, it may be possible to easily install the membrane as a single section. However, in some cases, depth or instability of the subgrade may limit the amount of trench which can be open and maintained unobstructed at any time and in consequence require that the membrane be installed in a series of panels which must be jointed together within the trench. Other than in cases of broad open trenches where there is safe access for seaming, some form of mechanical interlock must be introduced to allow membrane panels of the appropriate width and depth to be installed consecutively with a joint which resists permeation to a degree consistent with the design objectives of the project.
The panel size may be limited by the length of an unsupported trench which can remain open for the installation. The degree of curvature of the trench and the angle of repose of backfill material must also be considered. Relatively short panels can easily be lifted vertically with a crane or hoisted and dropped or inserted into position. A framework of rigid materials may be employed to assist with the positioning of the membrane panel. The framework also serves to help resist the effects of wind as the panel is lifted. In some instances, the panel may be too long and/or wide to install with a vertical lift. In many instances, wind and/or limited head room or other obstructions may interfere with the vertical lift.
FIGS. 1A and 1B serve to illustrate the prior art technique for the installation of such flexible panels. As can be seen in FIGS. 1A and 1B, the usual approach is to suspend the panel 10, with suitable stiffening of the upper edge, above the trench 12 using a crane 14 or similar lifting equipment. The lock 16 along a vertical edge of the suspended panel 10 is entered into the lock 18 of the panel 20 already in place. The suspended panel 10 is then lowered into the trench 12. The leading edge of the in place panel 20 may be braced so as to hold it firmly in place during the fitting of the subsequent panel 10. Weights, stiffeners and/or cable arrangements may be attached to the panels so as to provide downward forces during installation. These items may also be used to assist with forming a seal or anchoring the panel in the desired position.
In FIGS. 1A, it can be seen that the suspended panel 10 is generally entered centrally into the trench 12. As can be seen, the trench 12 has a relatively narrow opening in comparison with the depth of the trench. The panels are continually installed, as shown in FIGS. 1B, until the entire length of the trench is filled with the panels.
One of the great difficulties with the installation technique, shown in FIGS. 1A and 1B, is the fact that a great deal of equipment is required for installation. When steel carrying frames are required to facilitate the installation of the panel 10, then additional expense and complication are involved. In situations where a frame must receive the panel 10, prior to installation, then the frame must be continually moved during the installation of each of the panels. Alignment must be achieved between the crane 14, any frames, and the panels 20 which are already in place. This is a highly complicated, slow, and expensive procedure. Wind can create great difficulties during this type of installation procedure. Additionally, overhead obstructions may restrict the amount of vertical lift that can be attained. In some situations, these overhead obstructions may have to be dismantled and reinstalled. Since precise alignment is required for each of the panels, a great deal of human manipulation is required so as to properly align the panels during installation. The soil conditions and characteristics adjacent to the trench may prohibit the close proximity of heavy equipment to the open trench if the trench is to remain open.
It is an object of the present invention to provide an apparatus and method for the installation of flexible panels which is relatively simple and easy to operate.
It is a further object of the present invention to provide an apparatus and method for the installation of flexible panels which requires a minimal amount of equipment.
It is still a further object of the present invention to provide an apparatus and method for installing a flexible panel which avoids wind effects.
It is another object of the present invention to provide an apparatus and method which permits installation without interferences from most overhead obstructions.
It is an additional object of the present invention to reduce the load on the soil adjacent to the open trench.
It is still a further object of the present invention to provide an apparatus and method for installing a flexible panel which greatly speeds the installation procedure and improves the overall efficiency of installation.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.